1. Field of the Invention
The present invention relates to an image sensor for use in a small size facsimile device the like, and more particularly, to a complete-contact type image sensor capable of reading an original without reducing its size.
2. Description of the Prior Art
Since a contact type image sensor is capable of reading an original without using a reducing optical system, it has a shorter optical path and the sensor itself can be miniaturized. Therefore, sure a sensor is widely used in such reading apparatuses as small size facsimile device and bar code readers.
Among contact type image sensors in the prior art, there is one which uses, instead of a reducing optical system, an actual-size optical system represented by a SELFOC lens system, thereby forming an image on the sensor elements. Alternately, in order to lower the cost of the contact type image sensor, there has been developed a contact type image sensor of a system in which the SELFOC lens is not used, but instead the sensor elements are adapted to be brought into close contact with the original for reading an image. Hereinafter, the contact type image sensor of such a system will be denoted a "complete-contact type image sensor".
A complete-contact type image sensor includes a glass substrate, sensor elements formed on the glass substrate, input contact members connected with the sensor elements at their input side, output contact members connected with the sensor elements at their output side, driving ICs for driving the sensor elements, a light source disposed in the rear of the sensor elements, a roller to press an original against the sensor elements, and a casing for housing the sensor elements and the like. The input contact members are provided by patterning on the glass substrate set to one side and the output contact members are provided by patterning thereon set to the other end portion and the sensor elements are formed between both the contact members (Japanese Laid-open Patent Publication No. 62-126665).
A light beam emitted from the light source is reflected by the original and introduced into the sensor elements to be converted into electric signals. The driving ICs sequentially drive a large number of the sensor elements formed on the glass substrate through the output contact members and input contact members and read the electric signals photoelectrically converted by the sensor elements.
The complete-contact type image sensor (hereinafter to be also denoted simply as a "sensor") is desired to be arranged such that the distance between the original and the sensor elements is kept as small as possible because the resolution deteriorates if the original is held apart from the surface of the sensor elements. In the prior art sensor, the sensor elements are formed virtually in the center on the glass substrate and the input contact members and the output contact members are formed at opposite side end portions on the glass substrate with the sensor elements therebetween. In such a prior art sensor, there are formed protruded portions on the glass substrate at both its side end portions due to the presence of the contact members with the sensor elements disposed between these protrusions. Hence, if the width of the glass substrate is small, it is difficult to bring an original into close contact with the sensor elements. There has therefore been a problem with the prior art small-sized complete-contact type image sensor is that its MTF (Modulation Transfer Function) is rather inferior.
Further, since the input contact members and the output contact members are formed apart at opposite side end portions on the glass substrate in the prior art complete-contact type image sensor, if the distance between the input contact members and the output contact members is small, the roller comes into contact with holders covering the contact members and the like when the roller operates to bring an original into the close contact with the sensor elements. Therefore, in the prior art complete-contact type image sensor, it has been necessary to use a relatively wider glass substrate to space the input contact members and the output contact members sufficiently apart from each other, and this has made it difficult to miniaturize the module of the total sensor elements including both the contact members.